Electric power cable



Jan. 16, 1940. H. MILLIKEN mmc'nuc rowan CABLE Filed June 1, 1937 INVENTOB HUMPHBEYS MILLIKEN ATTORNEY Patented Jan. 16, 1940 UNITED; STATES.

PATENT OFFICE 1 Claim.

This invention relates to electric power cables for carrying large alternating currents and has for its object to reduce the loss in efiiciency due to the phenomenon known as skin eiiect.

5 In my prior United States Patent 1,904,162 I have disclosed several examples of cables in which loss of efliciency due to skin effect is substantially reduced by laying the cable strands so that, insofar as is practically possible, each strand occupies successively every strand position in the cross section of the cable foran equal distance along the length of the cable.

Each strand is thus subjected to substantially the same total inductive efiect as every other 13 strand and therefore carries substantially the same total quantity of current. In cables of this character the efiiciency depends upon each strand being insulated to some degree to prevent or reduce the flow of current from strand to strand. As pointed out in my prior patent such insulation may consist merely of that resulting from the natural oxidation of the surface of the strands which introduces contact resistance between the strands and thus reduces, to some extent, the flow of current from strand to strand. An alternative method also suggested in my prior patent is the application of a cotton covering to each strand to completely eliminate the flow of current from strand to strand. In

90 actual practice neither of these methods have proven entirely satisfactory. The first is the least expensive but is characterized by minimum eiilciency. The second gives maximum eiiiciency but at maximum cost.

The present invention is based on the discovery of a simple and comparatively inexpensive method of insulation whereby the flow of 1 current from strand to strand in cables made in accordance with my prior patent may be completely prevented without resorting to the expensive practice of applying a wrapping of insulating material to each individual strand. Briefly stated, the improved method consists in (l) interposing a layer of insulation such as thin paper tape between adjacent layers of the strands and (2) enclosing. one strand in each layer within a covering of cotton or other suitable insulating material.

It is not absolutely essential to the purpose of this invention that one strand of eachlayer be completely covered with cotton or other insulating material since the same results may be obtained by laying a continuous strip of insulation between any two strands in the same layer.

The provision of a cotton covered strand in each layer is, however, preferred as the more practical method of holding the required insulation in place.

Proceeding now to a more detailed description of this invention reference will be had to I the accompanying drawing, in which- Fig. l is a cross-sectional perspective view of a cable made in accordance with this invention.

Fig. 2 is a view similar to Fig. 1 but showing a slightly modified application of the insulating 10 means.

Fig. 3 is a side view of a complete cable with the covering broken away for better illustration.

The cable appearing in Fig. 1 is divided into four identical segments insulated from each other 15 as indicated at A. Each segment consists of a. number of concentric layers of strands, the strands of each layer being laid together helically as described in my prior patent so that each strand in any one layer occupies, in turn,

posed layer B of insulation such as thin paper 30 tape. One strand C in each layer of each segment is also completely insulated from the adjacent strand in the same layer by an insulating covering D of cotton or similar insulating material. Each covered strand, by reason of its 35 helical path, forces the current in all the strands in the same layer to follow the helical path through the interior of the cable, thus giving the same current per strand through the interior as through the exterior of the cable. This eliminates skin effect as completely as if every strand in the cable were provided with the insulation D. The insulation provided between the several layers of each segment is necessary to prevent the shunting of current around the cotton covered strand by contact with bare strands of the adjacent layers.

Instead of completely enclosing one strand in each layer ,in a covering of cotton or similar insulating'material the same result may be accomplished by laying a continuous strip of insulation E between any two strands in each layer as shown to advantage in Fig. 2.

Since the insulation above described has greater eflfect in the outer layers of the seg- 55 cost and economy result in the omission of such insulation from the centremost layers. This is feasible and would still provide a cable which is a substantial improvement over that disclosed in my prior patent.

All the wires and sectors of the cable are of the same polarity and are connected together electrically at each end of the cable as indicated at d in Figure 3.

Having thus described my invention, what I claim is:

A cable for alternating'power currents composed of a plurality of sectors helically arranged around the axis of said cable, each sector being insulated from the adjacent sectors by an interposed layer of insulating material and being composed of a plurality of layers of solid wires, the component wires of each layer being continuous throughout the entire length of the cable and being separated from the component wires in the adjacent layer or layers by an interposed layer of insulating material, each wire continuing in the same layer throughout the length of the cable and being helically arranged around the axis of its segment, all of said wires and sectors being of the same polarity and connected together electrically at each end of the cable, said cable being further characterized in that only a few wires in each layer are insulated from each other, the remaining wires in said layen being left bare and disposed in contact with each other.

HUMPHREYS MILIJKEN. 

